linux-kernel - Re: chroot(2) and bind mounts as non-root

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Message-ID: <4EDFCDD4.2080603@zytor.com>
Date:	Wed, 07 Dec 2011 12:34:28 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Colin Walters <walters@...bum.org>
CC:	LKML <linux-kernel@...r.kernel.org>, morgan@...nel.org,
	serue@...ibm.com, dhowells@...hat.com, kzak@...hat.com
Subject: Re: chroot(2) and bind mounts as non-root

On 12/07/2011 09:54 AM, Colin Walters wrote:
> 
> The historical reason one can't call chroot(2) as non-root is because of
> setuid binaries (hard link a setuid binary into chroot of your choice
> with trojaned libc.so).

No.  The historical reason is that it lets anyone escape a chroot jail:

	mkdir("jailbreak", 0666);
	chroot("jailbreak");

	/* Now the cwd is outside the root, and therefore not bound by
           it, walk the chain of .. directories until they don't change
           anymore */

	chroot(".");	/* Change the root to the system root */

Oops.

	-hpa


	
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